The present invention relates to a digital image forming apparatus for forming an image on an image carrier in response to input image data.
One of conventional digital copiers, printers or similar image forming apparatuses generates image data to be written in response to image data sent from an input device, exposes the precharged surface of a photoconductive element, or image carrier, on the basis of the image data to electrostatically form a latent image, and develops the latent image by a toner. This type of apparatus often uses a light emitting diode (LED) array as means for exposing the photoconductive element. An LED array implements high-speed printing and broad-width printing, compared to laser optics which scans a photoconductive element by a single laser beam. Further, since the LED array extends in the main scanning direction, it insures high positional accuracy in the main scanning direction on the photoconductive element.
In parallel with the spread of digital image forming apparatuses, there is an increasing demand for high image quality in the total sense. There is also a keen demand for outputting methods each matching a particular kind of image due to the diversifying input system and diversifying document image. One conventional approach for meeting such demands is to change the pixel density of an image to be written in the photoconductive element by the exposing means. Laser optics, for example, changes the pixel density of an image by reducing the spot size of the laser beam and subjecting the laser beam to various kinds of modulation. However, since laser optics forms an image by manipulating a single beam, it cannot change the pixel density unless the construction thereof is drastically changed. Moreover, it is difficult with such laser optics to control the writing position on the photoconductive element. Laser optics with a special configuration would increase the size and cost of the entire apparatus.